Glob top encapsulation using molding tape

ABSTRACT

A lead frame used to assemble a semiconductor device, such as a smart card, has a first major surface including exposed leads and a second major surface including a die receiving area and one or more connection pads surrounding the die receiving area. The connection pads enable electrical connection of an Integrated Circuit (IC) die to the exposed leads. A molding tape sized and shaped like the lead frame is adhered to and covers the second major surface of the lead frame. The molding tape has a die receiving area cut-out that exposes the die receiving area and the connection pads on the second major surface of the lead frame and forms a cavity for receiving an encapsulant. The cut-out has an elevated sidewall for retaining the encapsulant within the cavity.

BACKGROUND

The present invention relates generally to techniques for assemblingintegrated circuit (IC) devices and, more particularly, to techniquesperforming a molding or encapsulating process in IC device assembly.

Encapsulation is a standard semiconductor process used to providephysical, chemical, and electrical protection to an IC die. Typically,the encapsulation process covers the entire surface of the die as wellas any electrical connections to the die. One encapsulation processcommonly used for smart card assembly, for example, is glob top molding,which is an inexpensive and easily automated process. In glob topmolding, there is a single resin glob top process and a two-resin, “Damand Fill” process. In the single resin process, a thixotropic glob topmaterial is dispensed over the die and wirebonds and cured, while in thedam and fill process, a highly thixotropic “dam” material is dispensedaround the area to be encapsulated and then the “dam” is filled with alower viscosity material that covers the die and wirebonds.

FIG. 1A is a top plan view of a conventional lead frame 10 used in smartcard assembly. The lead frame 10 has a first side with exposed metalcontacts 12. FIG. 1B is a bottom view of the lead frame 10, which has anepoxy surface 14, conductive traces that form an antenna 16 and holes 18that are used to provide a path to the metal contacts 12. There also isa die receiving area 20 located within an area defined by the holes 10.FIG. 1C shows the bottom side of the lead frame 10 after a die has beenattached and electrically connected to the contacts 12 with bond wiresand then covered with an encapsulant 22. However, as can be seen, afterdispensing, the size and shape of the glob top material, i.e., theencapsulant 22 has not been controlled very well, and as shown in theinset, one of the bond wires 24 is exposed.

Both the single resin and two resin glob top processes often encounterproblems like the one shown in FIG. 1C, where the size and shape of theglob top is not uniform or well controlled, because the low viscosityresin material is not easy to control. Some other issues encountered areincomplete glob top, exposed die, exposed wire, glob top dimensions donot conform to package outline specifications, and the glob top may beoffset.

Accordingly, it would be advantageous to have an improved glop topencapsulation process that overcomes the above-listed defects.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will become more fully apparent from thefollowing detailed description, the appended claims, and theaccompanying drawings in which like reference numerals identify similaror identical elements.

FIG. 1A is a top plan view of a conventional lead frame used in smartcard assembly, FIG. 1B is a bottom plan view of the lead frame of FIG.1, and FIG. 1C is an illustration of the lead frame of FIGS. 1 and 2after an encapsulation process;

FIG. 2A is a top plan view of a lead frame used in smart card assemblyin accordance with an embodiment of the present invention, FIG. 2B is abottom view of the lead frame of FIG. 2A, and FIG. 2C is a top plan viewof a partially assembled smart card in accordance with an embodiment ofthe present invention;

FIG. 3A illustrates how a piece of tape of the present invention relatesto a lead frame, FIG. 3B illustrates the piece of tape used to assemblea smart card in accordance with an embodiment of the present invention,and FIG. 3C is a greatly enlarged view of a portion of the piece of tapeof FIG. 3A;

FIGS. 4A, 4B and 4C illustrate various alternative embodiments of thepiece of tape of FIG. 3B;

FIGS. 5A and 5B also illustrate alternative embodiments of a piece oftape used in a glob top molding process in accordance with the presentinvention;

FIG. 6 illustrates steps in a smart card assembly process in accordancewith an embodiment of the present invention; and

FIGS. 7A and 7B illustrate a strip of lead frames including a moldingtape in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Detailed illustrative embodiments of the invention are disclosed herein.However, specific structural and functional details disclosed herein aremerely representative for purposes of describing example embodiments ofthe invention. The invention may be embodied in many alternate forms andshould not be construed as limited to only the embodiments set forthherein. Further, the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of example embodiments of the invention.

As used herein, the singular forms “a,” “an,” and “the,” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It further will be understood that the terms “comprises,”“comprising,” “includes,” and/or “including,” specify the presence ofstated features, steps, or components, but do not preclude the presenceor addition of one or more other features, steps, or components. It alsoshould be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

In one embodiment, the present invention is a lead frame having a firstmajor surface with a plurality of exposed contacts and a second majorsurface having a die receiving area and one or more connection padssurrounding the die receiving area. The connection pads enableelectrical connection of an Integrated Circuit (IC) die to the exposedcontacts. A molding tape sized and shaped like the lead frame is adheredto and covers the second major surface of the lead frame. There is a diereceiving area cut-out in the molding tape that exposes the diereceiving area and the connection pads on the second major surface ofthe lead frame and forms a cavity for receiving an encapsulant. Thecut-out includes an elevated sidewall for retaining the encapsulantwithin the cavity.

In another embodiment, the present invention is a smart card comprisinga lead frame, a molding tape, an IC die and an encapsulant. The leadframe has a first major surface with a plurality of exposed contacts anda second major surface having a die receiving area and one or moreconnection pads surrounding the die receiving area. The connection padsenable electrical connection of the IC die to the exposed contacts. Themolding tape is sized and shaped like the lead frame, and is adhered toand covers the second major surface of the lead frame. The molding tapeincludes a die receiving area cut-out that exposes the die receivingarea and the connection pads on the second major surface of the leadframe and forms a cavity for receiving an encapsulant. The cut-outincludes an elevated sidewall for retaining the encapsulant within thecavity. The IC die is attached to the die receiving area and bondingpads on an upper surface of the IC die are electrically connected withrespective ones of the connection pads using bond wires such that the ICdie is electrically connected to the exposed contacts. The encapsulantis dispensed within the cavity and covers the IC die and the bond wiresand thereby forms a glob top. The elevated sidewall prevents theencapsulant from spilling out of the cavity and onto the second majorsurface of the lead frame.

In yet another embodiment, the present invention provides a method ofassembling a smart card. The method includes attaching an IC die to adie receiving area of a lead frame, where the lead frame has a firstmajor surface with a plurality of exposed contacts and a second majorsurface having the die receiving area and one or more connection padssurrounding the die receiving area. The connection pads enableelectrical connection of the IC die to the exposed contacts. A moldingtape sized and shaped like the lead frame is adhered to and covers thesecond major surface of the lead frame. The molding tape includes a diereceiving area cut-out that exposes the die receiving area and theconnection pads on the second major surface of the lead frame and formsa cavity for receiving an encapsulant. The cut-out includes an elevatedsidewall for retaining the encapsulant within the cavity. The methodfurther includes electrically connecting the IC die with the exposedcontacts by way of the connection pads and dispensing a liquidencapsulant into the cavity such that the encapsulant covers the IC dieand the electrical connections of the IC die to the connection pads.

Referring now to FIGS. 2A and 2B, top and bottom views of a lead frameassembly 100 in accordance with an embodiment of the present inventionare shown. The lead frame assembly 100 includes a lead frame, such asthe lead frame 10 shown in FIGS. 1A and 1B, and a molding tape. FIG. 2Ashows a contact side of the lead frame assembly 100. The contact sidecomprises a first major surface of the assembly 100 and has a pluralityof exposed contacts 102. The lead frame and lead frame assembly 100 alsohave a plurality of holes 104 that are used to position the lead frameand lead frame assembly during processes such as die attach and wirebonding.

FIG. 2B shows an encapsulation side of the lead frame assembly 100,which is a second major surface of the lead frame like the conventionallead frame 10 shown in FIG. 1B except that here, the second majorsurface is covered with a molding tape 106. The molding tape 106, whichis sized and shaped like the lead frame, has an adhesive on one sidesuch that it adheres to the second major surface of the lead frame. Themolding tape 106 includes a die receiving area cut-out that exposes adie receiving area 108 and connection pads 110 on the second majorsurface of the lead frame. The die receiving area cut-out also forms acavity for receiving an encapsulant, as will be discussed in more detailbelow. Also, as will be discussed in more detail below, the diereceiving area cut-out includes an elevated sidewall for retaining theencapsulant within the cavity.

The connection pads 110 enable electrical connection of an IC die to theexposed contacts 102 on the contact side of the lead frame. In someembodiments, the lead frame includes an antenna 112 and in suchembodiment, the molding tape 106 includes another cut-out to expose theantenna.

The lead frame may be a multi-layer lead frame, for instance, comprisinga layer of conductive metal, one or more layers of non-conductivematerial, and conductive metal traces. In the lead frame assembly 100,the first major surface comprises exposed conductive metal and thesecond major surface comprises a non-conductive material, such as epoxyresin and/or epoxy glass. The conductive metal typically comprisesCopper that is plated with other metals such as Nickel, Gold and/orPalladium.

FIG. 2C shows an IC die 114 attached to the die receiving area 108 andelectrically connected to the connection pads 110 with bond wires 116,such that the die 114 is in electrical communication with the exposedcontacts 102. An encapsulant 118, which is dispensed within the cavity,covers the IC die 114 and the bond wires 116 and forms a glob top. Inthe drawings, the encapsulant 118 is shown as transparent, but this isjust so that the underlying components of the assembly may bevisualized. The encapsulant 118 typically is non-transparent. Theelevated sidewall of the cut-out prevents the encapsulant 118 fromspilling out of the cavity and onto the second major surface of the leadframe.

FIG. 3A shows the molding tape 106 being peeled off the encapsulationside of the assembly 100 and FIG. 3B shows just the molding tape 106. Inthe embodiment shown in FIGS. 3A and 3B, the lead frame does not includean antenna, so the molding tape does not include a corresponding cut-outfor an antenna. Thus, in this embodiment, the molding tape 106 includesa die receiving area cut-out 120 and a cut-out sidewall 122. In FIG. 3A,it can be seen that the placement of the encapsulant 118 is controlledby the molding tape 106, with the molding tape 106 preventing theencapsulant 118 from spilling onto the second major surface of the leadframe.

FIG. 3C is a greatly enlarged view of the elevated sidewall 122, whichin this embodiment, is shown in the inset to be L-shaped cross-section.The molding tape 106 has a first height labeled C, the sidewall has asecond height labeled B, and the sidewall has a thickness labeled A. Inthe presently preferred embodiment, the second height B is about twicethe first height C, and twice the thickness A. In one example, the firstheight C is 0.05 mm or greater, the second height B is 0.1 mm orgreater, and the thickness A is 0.05 mm or greater.

FIGS. 4A, 4B and 4C show alternative embodiments of the sidewall 122. InFIG. 4A, the angle formed where the sidewall 122 meets the body of thetape is curved or beveled instead of at 90°. In FIG. 4B, the angleformed where the sidewall 122 meets the body of the tape is greater than90°, such that there is a slope between the sidewall and the main bodyof the tape. In FIG. 4C, although the angle formed where the sidewall122 meets the body of the tape is around 90°, the inner part of thesidewall 122 that is exposed at the cavity is angled such that where thetape 106 meets the encapsulation side of the lead frame near to the diereceiving area has an acute angle. In other words, an inner wall of themolding tape that defines the cavity is slanted.

FIGS. 5A and 5B are perspective views of lead frames with a molding tapepartially peeled away (for ease of understanding the invention), wherein FIG. 5A the die receiving area cut-out 130 is rectangular and in FIG.5B the die receiving area cut-out 132 is hexagonal. It should beapparent that the molding tape is used to control the encapsulationshape and size on the encapsulation side of the lead frame.

FIG. 6 illustrates a method of assembling a smart card in accordancewith an embodiment of the present invention. Starting at the upper leftside of FIG. 6, in a first step 150, a lead frame for assembling a smartcard is provided. The lead frame is similar to a conventional smart cardlead frame and has a first side 152 with exposed contacts and a second,encapsulation side, except that the encapsulation side is covered with amolding tape 154. The molding tape 154 is sized and shaped like the leadframe and is adhered to and covers the second major surface of the leadframe. The molding tape 154 includes a die receiving area cut-out thatexposes the die receiving area and the connection pads on the secondmajor surface of the lead frame and forms a cavity for receiving anencapsulant. The cut-out includes an elevated sidewall for retaining theencapsulant within the cavity. In one embodiment, the tape is applied tothe lead frame by a lead frame supplier when the lead frame ismanufactured.

At step 156, an adhesive or die attach film (DAF) is placed in the diereceiving area on the encapsulation side of the lead frame, and at step158 a die is attached in the die receiving area using the adhesive orDAF. The adhesive is cured so that the die is securely attached to thelead frame. At step 160, the die is electrically connected to theconnection pads on the lead frame. In the presently preferredembodiment, a standard wire bonding process is used to attach bond wiresto die bonding pads and respective lead frame connection pads. At step162, a glob top encapsulation process is performed whereby a liquidencapsulant 164 is dispensed into the cavity such that the encapsulantcovers the IC die and the electrical connections (i.e., the bond wires)of the IC die to the connection pads. The encapsulant 164 is retainedwithin the cavity by the elevated sidewalls so that the encapsulant doesnot spill over onto the second major surface of the lead frame. At step168, which is optional, the molding tape may be removed. That is, thetape can be removed when the encapsulation material is completely cured.The tape can be removed by a peeling tape machine, which is aconventional device well known by those of skill in the art insemiconductor device assembly. Of course, the tape also could be removedother ways, such as manually. Finally, at step 170, a finished device isexpected.

FIG. 7A is a perspective view of a lead frame strip 180 with a moldingtape 182 adhered to one side of the lead frame strip, and FIG. 7B is atop plan view of a lead frame strip 184 that comprises the lead framestrip 180 and the molding tape 182. Thus, it will be apparent to thoseof skill in the art that the invention is practiced on multiple leadframes simultaneously.

As will be apparent to those of skill in the art, the concept of thepresent invention is to attach a molding tape with guiding holes and acavity with elevated sidewalls to control better either a single ortwo-resin glob top encapsulation operation to better control theresulting size and shape of the glob top. In one embodiment, the moldingtape is removed after temperature and UV curing. It will be understoodby those of skill in the art that the size and shape of the tape canvary depending on the size and shape of the lead frame and the die(s) tobe attached to the lead frame. Use of the tape allows low viscosity orliquid materials to be applied to a smartcard package, or other types ofpackages, such as MEMS packages. The molding tape is sized to conform tothe outline of the finished package.

The molding tape allows for vastly improved shape, size and thicknessfor glob top encapsulation. The cut-out may be circular, rectangular,triangular or even a complex shape for a desired glob top process.

Unless explicitly stated otherwise, each numerical value and rangeshould be interpreted as being approximate as if the word “about” or“approximately” preceded the value or range.

It will be further understood that various changes in the details,materials, and arrangements of the parts that have been described andillustrated in order to explain embodiments of this invention may bemade by those skilled in the art without departing from embodiments ofthe invention encompassed by the following claims.

In this specification including any claims, the term “each” may be usedto refer to one or more specified characteristics of a plurality ofpreviously recited elements or steps. When used with the open-ended term“comprising,” the recitation of the term “each” does not excludeadditional, unrecited elements or steps. Thus, it will be understoodthat an apparatus may have additional, unrecited elements and a methodmay have additional, unrecited steps, where the additional, unrecitedelements or steps do not have the one or more specified characteristics.

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of theinvention. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments necessarilymutually exclusive of other embodiments. The same applies to the term“implementation.”

The invention claimed is:
 1. An article of manufacture, comprising: alead frame having a first major surface with a plurality of exposedcontacts and a second major surface having a die receiving area and oneor more connection pads surrounding the die receiving area, wherein theconnection pads enable electrical connection of an Integrated Circuit(IC) die to the exposed contacts; and a molding tape sized and shapedlike the lead frame, wherein the molding tape is adhered to the secondmajor surface of the lead frame and covers said second major surface,wherein the molding tape includes a die receiving area cut-out thatexposes the die receiving area and the connection pads on the secondmajor surface of the lead frame and forms a cavity for receiving anencapsulant that covers the die and the connection pads within thecavity, and wherein the cut-out includes an elevated sidewall forretaining the encapsulant within the cavity, wherein the molding tapehas a first height above the second major surface and the elevatedsidewall has a second height above the second major surface, wherein thesecond height is higher than the first height.
 2. The article of claim1, further comprising: an IC die attached to the die receiving area; anda plurality of bond wires electrically connecting bonding pads on anupper surface of the IC die with respective one of the connection padssuch that the IC die is electrically connected to the exposed contacts.3. The article of claim 2, further comprising the encapsulant dispensedwithin the cavity and covering the IC die and the bond wires and therebyforming a glob top, wherein the elevated sidewall prevents theencapsulant from spilling out of the cavity and onto the second majorsurface of the leadframe.
 4. The article of claim 1, wherein the cavityis ring shaped.
 5. The article of claim 1, wherein the cavity is one ofring shaped, rectangular, and hexagonal.
 6. The article of claim 1,wherein the elevated sidewall has an L-shaped cross-section.
 7. Thearticle of claim 6, wherein the second height is about twice the firstheight.
 8. The article of claim 7, wherein a thickness of the sidewallis about the same as the first height.
 9. The article of claim 6,wherein an angle formed where an outer side surface of the sidewallmeets an exposed upper surface of the molding tape is beveled.
 10. Thearticle of claim 6, wherein an angle formed where an outer side surfaceof the sidewall meets an exposed upper surface of the molding tape isgreater than 90°.
 11. The article of claim 6, wherein an inner wall ofthe molding that defines the cavity is slanted.
 12. The article of claim11, wherein the angle formed where the inner wall of the molding tapesmeets the second major surface of the lead frame is less than 90°.
 13. Asmart card, comprising: a lead frame having a first major surface with aplurality of exposed contacts and a second major surface having a diereceiving area and one or more connection pads surrounding the diereceiving area, wherein the connection pads enable electrical connectionof an Integrated Circuit (IC) die to the exposed contacts; a moldingtape sized and shaped like the lead frame, wherein the molding tape isadhered to the second major surface of the lead frame and covers saidsecond major surface, wherein the molding tape includes a die receivingarea cut-out that exposes the die receiving area and the connection padson the second major surface of the lead frame and forms a cavity forreceiving an encapsulant, and wherein the cut-out includes an elevatedsidewall for retaining the encapsulant within the cavity, wherein themolding tape has a first height above the second major surface and theelevated sidewall has a second height above the second major surface,wherein the second height is higher than the first height, an IC dieattached to the die receiving area; a plurality of bond wireselectrically connecting bonding pads on an upper surface of the IC diewith respective one of the connection pads such that the IC die iselectrically connected to the exposed contacts; and the encapsulantdispensed within the cavity and covering the IC die and the bond wiresand thereby forming a glob top, wherein the elevated sidewall preventsthe encapsulant from spilling out of the cavity and onto the secondmajor surface of the lead frame.
 14. The smart card of claim 13, whereinthe cavity is ring shaped and the elevated sidewall has an L-shapedcross-section.
 15. The smartcard of claim 14, wherein the second heightis about twice the first height.